While there is still no single, universally standardized way to measure biological age, this particular study examined a range of clinical and metabolic markers—including insulin levels, blood pressure, and cholesterol—to determine the functional age of the subjects’ cells. Based on the findings, making certain nutritional adjustments can have a profound impact, and in a remarkably short amount of time, particularly when those adjustments involve diets of the higher-carbohydrate variety.
Biological age has become a major focus in scientific research and general health conversations of late. As many health enthusiasts and researchers alike understand, biological age measures how old your cells, tissues, and bodily systems actually are, whereas chronological age is simply the number of years you have been alive. Biological age, which is heavily influenced by factors such as chronic bodily inflammation and underlying diseases and conditions, has increasingly shown up in everything from consumer health trackers to complex academic research studies.
However, its practical usefulness outside of casual cocktail conversation is still actively being explored by the medical community. You certainly will not find your family doctor relying solely on this metric during a routine annual physical just yet.
To dig deeper into the relationship between diet and cellular aging, researchers at the University of Sydney recruited 104 healthy adults in their mid-60s and 70s and randomly assigned the participants to follow one of four distinct diets for a period of four weeks. It is worth noting that the study was relatively small in scale, with only 26 participants assigned to each dietary group.
Each person in the trial was asked to ingest precisely 14 percent of their total daily calories from protein while adhering to their assigned regimen. Two of the four diets were omnivorous—meaning participants consumed foods from an equal and balanced mix of plant and animal sources—and two were semi-vegetarian diets, where 70 percent of the dietary protein came strictly from plant-based sources. Within these protein frameworks, participants were then asked to follow either a higher-fat, lower-carbohydrate eating pattern or a lower-fat, higher-carbohydrate eating pattern.
When the results were analyzed, the most striking impact on biological age biomarkers seemed to occur in the participants who followed an omnivorous, high-carbohydrate diet. The participants in that specific group obtained 14 percent of their daily calories from protein, up to 29 percent of their calories from fat, and a robust 53 percent from carbohydrates. According to the study parameters, the carbohydrates in all of the experimental diets were primarily composed of complex carbohydrates derived from whole, minimally processed food sources rather than refined sugars and white flours.
By contrast, the omnivorous, high-fat diet—which most closely resembled a traditional Western diet among the four options—was the most similar to the way the participants had been eating before the clinical study even started. Health-care providers and researchers often use the term Western diet to describe an eating pattern characterized by high levels of refined grains, red and processed meats, ultra-processed foods, deep-fried items, and high-fat dairy products.
That particular diet contained fewer servings of fruits, vegetables, and legumes than the other three experimental regimens, even though it shared the same minimally processed carbohydrate sources. The researchers ultimately found no meaningful change in the estimated biological age of those participants after the four-week intervention period.
However, people in the other three dietary groups all experienced notable reductions in their estimated biological age based on their blood biomarkers. Researchers emphasize that these are years of estimated biological age, not literal years of extended life; essentially, it means the subjects’ blood test results looked remarkably like those of a younger person. Furthermore, because the intervention period was relatively short-term, experts caution that we cannot be entirely certain the observed shifts reflect real, permanent changes in the overall rate of aging.
Carbohydrates seem to be quietly coming back into favor elsewhere in the scientific literature as well. New research out of the Tabriz University of Medical Sciences, published in the European Heart Journal, recently linked eating up to six servings of whole grains a day—roughly equivalent to six slices of whole-grain toast—with lower cholesterol levels, improved blood sugar regulation, and reduced body weight. All of these factors are known to heavily influence overall metabolic and biological age.
Even so, professional dietitians and nutritionists urge caution and nuance before anyone rushes out to order a heavy bowl of carbonara or a basket of white bread rolls in the name of cellular longevity.
Why Might a High-Carbohydrate Diet Reduce Biological Aging?
It remains difficult to determine precisely what these biomarker changes mean in terms of actual biological aging in the real world beyond the controlled environment of a clinical study.
"I wouldn’t necessarily look at this as an age reversal," says Jessica Cording, a registered dietitian and author of The Little Book of Game-Changers. The researchers themselves also took care to write in the published study that "caution is warranted in interpreting such changes as evidence of biological age reversal."
Even the study’s primary researchers are hesitant to apply an actual number of biological years gained or lost based strictly on these findings.
"These are years of estimated biological age, not years of life, so it means the blood results looked like those of a younger person," explains Caitlin J. Andrews, PhD, a study co-author and researcher at the University of Sydney’s School of Life and Environmental Sciences.
Nutrition experts point out that the type of carbohydrate matters immensely. "Eating more carbs may also mean higher intake of fiber from plant foods, but not necessarily," says Sandra Zhang, RDN, LDN, a registered dietitian and nutritionist at the Frances Stern Nutrition Center at Tufts Medical Center.
Jessica Cording agrees, noting that all carbohydrates are certainly not created equal in the human body. "People tend to think of bread, rice, pasta, and sugar as carbs, but they often forget that vegetables, fruit, nuts, seeds, and legumes also have carbohydrates," she explains.
These foods offer a wide array of protective nutrients, including essential vitamins and powerful polyphenols that support healthy aging over the long term, she points out. This particular University of Sydney study specifically focused on high-quality, complex carbohydrates like the ones Cording listed.
"This could be reflecting more whole foods in a person’s diet," Cording says. "It’s not just about the carbs."
While dividing up a diet strictly by its underlying macronutrients is a convenient way for researchers to categorize an eating routine, Zhang notes that good nutrition is ultimately much more complex than simple percentages.
"Different types of fats, carbohydrates, fiber, and protein intake can also influence the inflammation process," she says.
The overall quality of the diet matters significantly, according to Dr. Andrews. "The benefits across the study tended to be associated with the diets that moved further away from a typical Western diet toward more minimally processed, whole food diets," she notes.
What the Findings Mean for a Healthy Daily Diet
When it comes to structuring a sustainable, health-promoting diet, variety is the ultimate key to longevity, according to Zhang. That means including different types of healthy fats from both animal and plant origins, and trying to feature a wide, colorful range of nutrients on your plate at every meal.
"Plant-based proteins do carry the benefits of low-fat and high-fiber, but they are not necessarily easily absorbed and complete, especially for the elderly," Zhang cautions.
That is precisely why Cording suggests maintaining a healthy balance of both plant-based and animal-derived proteins rather than cutting out entire food groups.
"Make room for beans, nuts, and seeds, along with lean meats. There is room for all of it," she says. "You want an overall diet pattern that gives you a good balance of protein, fats, and carbohydrates."
People have been deeply wary of carbohydrates for years, largely due to the popularity of low-carb and ketogenic dieting trends, but these latest findings suggest there is still a very valid, healthy place for this macronutrient—provided you choose your sources wisely.
"Foods like vegetables, fruits, legumes, and whole grains tend to be higher in fiber, more filling, and associated with better long-term health than more heavily processed, carbohydrate-rich foods," Dr. Andrews says. "More broadly, I think there’s a lot to be said for shifting the focus away from strict food restriction and more toward overall dietary quality and balance."
More conventional nutritional wisdom, such as actively limiting ultra-processed foods and excess added sugars, remains just as crucial for healthy aging, Cording adds.
"I tend to recommend a plant-forward Mediterranean-style diet," she explains. This type of eating pattern typically includes a generous mix of high-quality carbohydrates, such as brown rice, lentils, and beans, with up to 60 percent of total daily calories coming from these nutrient-dense sources.
Overall, the findings serve as a solid, encouraging reminder that it is never truly too late to make positive changes to your daily diet.
"The researchers saw that short response time; four weeks is nothing," Cording says. "It reinforces that you don’t need to eat perfectly for years before your body starts to benefit from you making better food choices."
